This invention relates to optical fibers, and, more particularly, to a method of testing the payout of an optical fiber from a support upon which it is wound.
Optical fibers for information transmission are strands of glass fiber processed so that light transmitted through the fiber is subject to total internal reflection. A large fraction of the incident intensity of light directed into the glass fiber is received at the other end of the fiber, even though the glass fiber may be many thousands of meters long. Optical-quality glass fibers have shown great promise in communications applications, because a high density of information may be carried along the glass fiber and because the quality of the signal is less subject to external interferences of various types than are electrical signals carried on metallic wires. Moreover, the glass fibers are light in weight and made from a plentiful substance, silicon dioxide.
The glass fibers are fabricated by preparing a preform of glasses of the two different optical indices of refraction, one inside the other, and processing the preform to a fiber. The optical glass fiber is coated with a polymer layer termed a buffer to protect the glass from scratching or other damage, and the resulting coated glass fiber is generally termed an "optical fiber" in the art. As an example of the dimensions, in a typical configuration the diameter of the glass fiber is about 125 micrometers, and the diameter of the glass fiber plus the polymer buffer (the optical fiber) is about 250 micrometers (approximately 0.010 inches).
For some applications, the optical fiber is wound onto a cylindrical or slightly tapered conical bobbin with many turns adjacent to each other in a side by side fashion. After one layer is complete, another layer of fiber is carefully laid on top of the first layer, and so on. The final assembly of the bobbin and the wound layers of optical fiber is termed a canister, and the mass of wound optical fiber is termed the fiber pack. When the optical fiber is later to be used, the optical fiber is payed out from the canister in a direction generally parallel to the axis of the cylinder.
The preparation of a canister demands great care and precision in winding of the optical fiber. The payout velocity of the optical fiber may be as high as several hundred to a thousand meters per second. If any snags, uneven stresses, or other irregularities are present, they can cause the optical fiber to snarl and/or break. One technique to avoid irregularities in the fiber pack is to utilize an adhesive on the optical fiber to hold each layer securely in place as the next layer is laid upon it. In one approach, a light coating of the adhesive is sprayed over a layer after it is wound onto the bobbin, prior to winding the next layer. In others, the bobbin may be dipped into a bath or the adhesive may be pre-applied to the optical fiber, for example.
The smooth payout of the optical fiber from the canister is dependent upon a number of factors, including the type and amount of adhesive, the winding tension of the optical fiber as it is wound upon the bobbin, the size and regularity of the optical fiber, and the rate of payout which is often over 300 meters per second. In evaluating the effects of parametric variations such as the precise formulation and amount of adhesive, it has been the common practice to wind a canister of at least a thousand meters or so of optical fiber. Payout is accomplished by catching a free end of the optical fiber on a rotating drum and "yanking" it from the canister. Measurements are made as the optical fiber is payed out, and these measurements are used to understand the effect of the variable under study.
This approach to testing is expensive because of the cost of the optical fiber and of the preparation of the completed canister. It also may be inaccurate due to unexpected variations in the optical fiber, the adhesive, or other parameters. There is a need for a more economical and reliable approach to testing the effect of variations in adhesive properties and other factors on the payout of optical fiber from a support. The present invention fulfills this need, and further provides related advantages.